Container for nuclear fuel transportation

ABSTRACT

A transport container for nuclear fuel is provided with an outer container having internal insulation, the insulation defining an internal cavity. The cavity receives a plurality of fuel containers wherein the internal volume of the fuel containers is at least 5% of the external volume of the outer container The container allows substantially higher volume proportions of enriched fuel to be safely transported than is possible with prior containers.

[0001] [01] This application is a continuation of U.S. patentapplication Ser. No. 09/180,029, entitled CONTAINER FOR NUCLEAR FUELTRANSPORTATION, filed May 7, 1999, which is U.S. nationalization ofInternational Application No. PCT/GB97/01197, and which claims priorityto Great Britain Application No. 9609304.2, filed May 3, 1996, whichapplications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. The Field of the Invention

[0003] [02] This invention concerns improvements in and relating to fueltransportation, particularly but not exclusively relating to enrichednuclear fuels.

[0004] 2. The Relevant Technology

[0005] [03] Nuclear fuels, such as enriched uranium or mixed oxideforms, frequently need to be transported between sites, for instance theenrichment site and the fuel rod production site. The fuel is normallyin the form of pellets or powder at this stage. International standardsapply, requiring certain levels of thermal insulation and structuralstrength. A major concern is criticality control. The mass of enrichedfuel within the transport container must be strictly limited to ensurethat a criticality event does not occur. This single requirement placesastringent limit on the volume of fuel which can be transported in anygiven volume of a transport container. In this regard, thetransportation of nuclear fuel differs significantly from transportationof other radioactive materials. Radioactive waste is of a far lowerenrichment, thus facilitating transport of greater volumes in proximitywith one another. In assembled fuel rods on the other hand, the volumeof fuel when compared with the overall fuel rod and supporting structurevolume is very low.

BRIEF SUMMARY OF THE INVENTION

[0006] [04] Present systems usually consist of a cylindrical drumprovided with one or more layers of wood on all sides, the wood defininga central recess into which a single cylinder containing the enrichedfuel is placed.

[0007] [05] The fuel containing volume of the inner drum is very lowcompared with the volume of the outer drum. As a consequence thetransportation of fuel takes up a considerable amount of space. Thecommercial considerations of this apply as they do to any transportationprocedure. Additionally the cylindrical nature of the unit presentshandling and stability problems.

[0008] [06] According to a first aspect of the invention we provide atransportable container for nuclear fuel, the container comprising anouter container provided with internal insulation, the insulationdefining an internal cavity, the cavity receiving a plurality of fuelcontainers, wherein the internal volume of the fuel containers is atleast 5% of the external volume of the outer container.

[0009] [07] A container having this level of fuel volume to overallvolume has not previously been achieved. The present invention alsoallows this level to be reached whilst meeting the necessarycriticality, insulation and other standards.

[0010] [08] Preferably the internal volume of the fuel container is atleast 10% of that of the external volume of the outer container. A levelof at least 15%, 20% or 25% is preferred. Levels of at least 30%, 35% oreven 40% may be reached. Any increase in fuel volume to overallcontainer volume is significant in reducing transportation costs and thecapital costs involved in providing the strong fuel containers.

[0011] [09] Preferably the outer container is formed with a steel andmost preferably stainless steel skin. The corners and/or edges of theouter container may be provided with strengthening elements. These maytake the form of L-shaped sections. The outer container is preferablyprovided with feet.

[0012] [010] The outer container is preferably provided with a lid. Thelid is preferably releasably fastened to the outer container Clampsattached to the outer container and releasably engageable with theperiphery of the lid are preferred. The clamps may also be releasablyengaged with the outer container. The lid may be provided with handlesor other forms of engagement for removal of the lid.

[0013] [011] It is particularly preferred that the lid be receivedwithin the perimeter of two or more projections from the outercontainer. The strengthening elements projecting above the top of thecontainer may define this perimeter.

[0014] [012] Preferably the insulating material is provided in a seriesof discrete layers. One or more base layers and/or one or more walllayers for each wall may be provided. The lid insulation may be mountedon the metal lid or may be provided separately. If provided separately apair of interlinking sections may be provided.

[0015] [013] The insulating layer is preferably thermally insulatingand/or neutron absorbing. Calcium silicate offers a preferred insulatingmaterial. One or more different materials may be used together or in asandwich style structure.

[0016] [014] Preferably the insulation layer defines the boundaries of asingle internal cavity. A rectilinear cavity is preferred.

[0017] [015] The internal cavity is preferably provided with acorrespondingly shaped single unit internal container comprising fourside walls and a base. The internal container is preferably made ofsteel, boronated steel, or most particularly stainless steel.

[0018] [016] In one form the internal container is preferably divided upinto a series of chambers. The chambers may be defined by one or moreelements crossing the internal cavity or container. Preferably theelements are plates spanning the full height, or at least substantiallythe full height, of the internal volume. Preferably one or more elementsspan the internal volume in different directions, most preferably atsubstantially 90 degrees to one another. Preferably the plates aresubstantially vertically provided. It is particularly preferred that twoplates cross the internal cavity in each of two directions at 90 degreesto one another. Preferably the internal volume is divided up into ninesubstantially equivalent chambers.

[0019] [017] In a second alternative form, the internal cavity may befitted with elements such as plates spanning the full height of theinternal volume to define an internal container. The chambers againbeing defined by one or more elements crossing the internal cavity. Abase plate may be provided on the base insulating layer to define a basefor the internal volume. A top plate may also be provided. Side platesmay also be provided to define the sides of the chambers.

[0020] [018] One or more of the base, top or dividing elements or platesmay be formed of metal. Steel and in particular stainless steel orboronated steel.

[0021] [019] The base, side and dividing plates or elements of thesingle unit internal container is alternatively provided as a separateunit to the insulating layers and outer container.

[0022] [020] In a further alternative form the internal cavity may befitted with a plurality of sleeve elements. Preferably the sleeveelements are adapted to receive fuel containers or pails. The sleevesmay be continuous or substantially continuous. Preferably the sleevesare of circular cross-section. Preferably the sleeves internal diameteris substantially equivalent to the external diameter of the fuelcontainers or pails. Preferably the sleeves are rigidly separated fromone another. The sleeves may be rigidly separated by mounting on a baseplate.

[0023] [021] Preferably the sleeves are discrete from one another aroundtheir entire periphery. Four or more, and preferably 8 or 9 such sleevesmay be provided within the internal cavity.

[0024] [022] The base plate may be attached to one or more side platesor elements. The side plates or elements may form walls corresponding tothe walls of the internal cavity. An internal container may thus beprovided.

[0025] [023] Preferably one or more of the sleeves are at least in partsurrounded by a neutron absorbing material. Preferably one or more ofthe sleeves, and most preferably all of the sleeves, are surrounded by aneutron absorbing material around their entire circumference. A neutronabsorbing material may optionally be provided around one or both ends ofone or more of the sleeves.

[0026] [024] Preferably the neutron absorbing material is a resin basedmaterial. Preferably the neutron absorbing material is fire resistant.Preferably the resin based material is loaded with, up to 6.5% boron, orup to 5% boron, and more preferably up to 2.5% boron. Preferably theresin occupies at least 50% of the non-sleeve volume of the internalcavity. The neutron absorbing material may fill the entire non-sleevevolume of the internal cavity or lower density materials may beincorporated, such as polystyrene.

[0027] [025] The internal container is preferably provided with a lid.

[0028] [026] Preferably the fuel containers or pails comprisecylindrical drums. Preferably releasable lids are provided. The releasemechanism for the lid is preferably contained within the plan profile ofthe container in the sealed position to minimise space.

[0029] [027] The fuel preferably occupies at least 50% of the fuelcontainer and may occupy 60, 70, 80, 90, 95% or any individual % valueover 50%.

[0030] [028] The fuel may be provided within the fuel containers inplastic bags, such as polythene.

[0031] [029] The fuel may be in pellet, powder or other form.Unirradiated enriched uranium may be the fuel. The provision of uraniumat substantially up to 5% enrichment may be used. A density of around1.4 g/cm³ may be used. In such a case each individual fuel container mayhave a volume of between 15 and 20 liters, for instance 17.3 liters.

[0032] [030] The boron content of any one of the insulator layers,internal divisions, sleeves, fuel containers, or remaining chamber spacemay be increased to give increased absorbtion.

[0033] [031] Fuel containers are preferably provided in more than threeof the chambers or sleeves. The provision of the fuel containers inperipheral chambers or sleeves and most preferably all the peripheralchambers or sleeves is envisaged. One or more of the chambers or sleevesmay be provided with a neutron absorber. Preferably the neutron absorberis provided in a unit corresponding in dimensions to the chamber orsleeve receiving it. The provision of polythene as the neutron absorberis preferred. The polythene absorber may be in a steel containercorresponding to the size and shape of the chamber or sleeve receivingit. The absorber may also be provided with a lid corresponding with thechamber or sleeve into which the absorber is placed in order to assistin retaining the absorber within the chamber or sleeve. The lid ispreferably of steel.

[0034] [032] In a particularly preferred form the container comprises anouter container with a removable lid, the outer container being providedwith an insulating layer on each wall and base, a further removableinsulating layer being provided between the lid and the internal cavityof the container in use, the internal cavity being divided into aplurality of chambers, a fuel container being provided in at least threeof the chambers and at least one of the chambers being provided with aneutron absorbing material.

[0035] [033] In an alternative particularly preferred form the containercomprises an outer container with removable lid, the outer containerbeing provided with an insulating layer on each wall and the base, afurther removable insulating layer being provided on the lid, theinsulating layers defining an internal cavity of the container, theinternal cavity being provided with a plurality of sleeves, a fuelcontainer being provided in at least 3 of the sleeves and the sleevesbeing at least partially surrounded by a neutron absorbing material.

[0036] [034] It is preferred that only one fuel container or pail beprovided in each chamber.

[0037] [035] A particularly preferred arrangement provides a rectangularplan aperture divided into nine chambers, three chambers by threechambers. Preferably the fuel containers are provided in the peripheralchambers. A neutron absorbing material may be substituted in the centralchamber and/or one or more of the other chambers as required.

[0038] [036] In a further particularly preferred arrangement arectilinear plan internal cavity may be provided with nine sleeveelements, in a three by three sleeve element arrangement. Preferablyfuel containers are provided in all the periphery sleeves and mostpreferably in all of the sleeves. A neutron absorbing material may besubstituted in one or more of the chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] [037] Various embodiments of the invention will now beillustrated, by way of example only, and with reference to theaccompanying drawings in which:

[0040] [038] FIG. 1 shows a perspective view of a container according toa first embodiment of the invention cut away to show the fuel containersin the container;

[0041] [039] FIG. 2 shows a cross-sectional side view of FIG. 1;

[0042] [040] FIG. 3 shows a pail load in plan view;

[0043] [041] FIG. 4 shows a side view of the container of FIG. 1;

[0044] [042] FIG. 5 shows a plan view of a closed container according tothe first embodiment of the invention partly cut away to show the fuelcontainers in the container of the invention;

[0045] [043] FIG. 6 shows one embodiment of a fuel container or pail foruse in the present inventions outer container;

[0046] [044] FIG. 6A shows a plan view of a fuel container or pail ofFIG. 6;

[0047] [045] FIG. 7 shows a perspective view of the container accordingto a second embodiment of the invention, cut away to show the fuelcontainers in the container;

[0048] [046] FIG. 8 shows a pail load in plan view; and

[0049] [047] FIG. 9 shows a cross-sectional side view along axis XX ofFIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] [048] The container as illustrated in FIG. 1 has the general formof a rectangular box. The container 1 is defined by four verticallyarranged walls 2 and a base wall 3. The walls are provided at the cornerjoins with strengthening elements 4 in the form of L-shaped strips. Thevertical strengthening elements 4 have portions 6 which extend beyondthe lid 8 of the container. Feet 10 are provided on each corner of thebase and engage with the portion 6 for easy and stable stacking.

[0051] [049] The outer skin forming the walls 2, base 3 and separate lid8 are made of stainless steel.

[0052] [050] A peripheral flange 12 is provided around the container.The lid 8 is dimensioned to be slidably received within the boundariesof the L-shaped elements 4. The lid 8 has a flange 16 which correspondswith the peripheral flange 12 of the container. Handles 14 on the lidaid in its removal and insertion.

[0053] [051] In the closed and retained position shown the lid 8 isretained by a series of quick release nuts and bolts 18 which engagecorresponding openings in the flange 16 of the lid 8. The lid isprovided with suitable seals to prevent any ingress of water.

[0054] [052] Next to the steel skin the container is provided with asubstantial thickness of a thermal insulator 20 formed from calciumsilicate. This layer is provided in a series of sections, see FIG. 2.The materials provision in solid sections ensures accurate positioningduring assembly and use. A single base layer of insulator 22 and fourwall sections 24 line the container itself. When the container isloaded, as described below, a two piece insulating top layer is applied.These two pieces 26, 28 are shaped to interconnect with one another.

[0055] [053] The rectangular box defined by the interior surfaces of theinsulating layers receives an internal container 30A having four wallsand a base and also made of boronated steel or stainless steel. Thiscontainer 30A is also provided with a lid 31 as shown in FIG. 1. As seenin FIG. 3 the container consists of a series of interlocking verticalwalls 30 made of boronated steel/stainless steel. The container 30A hastwo pairs of internal walls 30 at 90 degrees to one another definingnine chambers 32 within the pail load.

[0056] [054] In use within each of the eight peripheral chambers a fueldrum or pail 36 is received. The central chamber 32A is provided with apolythene neutron absorber 38. The absorber 38 is itself provided in asteel container (not shown) which corresponds with the shape of thechamber 32 into which it is to be fitted. A lid is provided on the topof the absorber to retain the absorber in place in the chamber 32A.

[0057] [055] Once the internal container 30A has received all eight fueldrums 36, and the container 1 is sealed by applying the lid 31, theinsulating top layer 26, 28, and the external lid 8. The lid 8 issecured to the container 1 by the quick release nuts and bolts 18.

[0058] [056] The fuel containing drum 36, as illustrated in FIG. 6,consists of a stainless steel cylinder wall 40 with a base plate 42 andreleasable lid 44. The lid 44 is provided with a standard internal leverclamp band 46 which enables the lid to be secured to the fuel drum 36.The provision of the internal lever clamp band 46 within the outline ofthe drum 36 is important to minimise the space taken up. In the closedstate the drum 36 is water tight avoiding any water ingress.

[0059] [057] The fuel 55 in either powder of pellet form is containedwithin polythene bags. The polythene bags filled with fuel are placed ina larger polythene bag which is placed in the drum. Once the larger bagis full this is then closed. The drum is then sealed with the lid 44.The fuel may typically be enriched uranium destined to form fuel rods.

[0060] [058] In the second embodiment of the invention illustrated inFIG. 7 the container 100 is once again in the form of a rectangular box.The external container 100 is defined in a similar manner to thecontainer of the first embodiment by vertically arranged side walls 102and a base wall 103. Other equivalent elements are numbered withreference numerals corresponding to those used in the first embodimentincreased by 100.

[0061] [059] Thus the strengthening elements, feet, peripheral flange,lid fixing and lid alignment are provided in a similar manner.

[0062] [060] The container 100 is also provided with substantialthickness of thermal insulator 120 provided by a base section, wallsections and a section optionally mounted on the lid in a similar mannerto the first embodiment of the invention.

[0063] [061] The arrangement within the internal cavity defined by theseinsulating layers differs, however.

[0064] [062] The cavity is provided with a series of stainless steelsleeves 150 which are rigidly mounted on a bottom plate standing on thebase layer insulation. The cylindrical sleeves are hollow and have aninternal dimension configured to snugly correspond to the externaldimensions of the fuel containers 152 shown inserted in the sleeves 150.Nine sleeves 150 are used in a three by three arrangement with a fuelcontainer 152 being positioned in each in use.

[0065] [063] The fuel containers are generally of the type illustratedin FIG. 6 and 6A above, but include external fasteners projecting beyondthe plan of the fuel containers.

[0066] [064] As shown in FIGS. 7, 8 and 9 the sleeves 150 are surroundedby a neutron absorbing material 158. This material is introduced to thevolume surrounding the sleeves during the manufacture of the portion ofthe assembly filling the internal cavity by pouring in a liquid resinwhich is then allowed to harden. A resin tight unit is preferred asdefining this cavity. The resin is loaded with boron preferably to alevel of 2% to provide the desired neutron absorbing capability. A boronloading up to 6.5 wt % and/or a lead loading up to 15 wt % may beprovided. The material offers between 1×10²² and 1×10²³ hydrogenatoms/cm³

[0067] [065] To reduce the cost and weight of the neutron absorbingmaterial, typically 1.68 g/cm³ lighter materials such as polystyrene canbe incorporated in portions where the neutron absorbing volume ofmaterial would otherwise be excessive. Thus at locations 162 betweensets of 4 sleeves and externally at the corner locations 164 andlocations 166 between the pairs of sleeves the neutron material may bereplaced with the lighter material. This does not affect the neutronabsorbing capability of the container.

[0068] [066] The fuel containing drums 152 and the manner in which thefuel, as powder or pellets is provided within them is as described abovefor the first embodiment of the invention.

[0069] [067] The present invention allows approximately 20% - 40% of theouter container volume to be occupies by fuel 55 and yet still meets thenecessary standards. This compares favourably with prior art systems. Anincreased payload is thus provided successfully.

[0070] [068] The use of stainless steel and the modular nature of theassembly assists in refurbishment and any cleaning stages required suchas decontamination.

What is claimed is:
 1. A transportable container for nuclear fuel, thecontainer comprising an outer container provided with internalinsulation, the insulation defining an internal cavity, the cavityreceiving a plurality of fuel containers, wherein the internal volume ofthe fuel containers is at least 5% of the external volume of the outercontainer.
 2. A container according to claim 1 in which the internalcavity is divided up into a series of chambers, the chambers beingdefined by one or more elements, the elements spanning substantially thefull height of the internal cavity and wherein fuel containers areprovided in more than three of the chambers.
 3. A container according toclaim 2 in which the internal cavity is divided into nine chambers,three chambers by three chambers, the fuel containers being provided inthe peripheral chambers and a neutron absorbing material being providedin the central chamber and/or one or more of the other chambers.
 4. Acontainer according to claim 2 in which the cavity is provided with ninesleeve elements, in a three by three sleeve element arrangement, todefine nine chambers, the fuel containers being provided in theperipheral chambers, a neutron absorbing material being provided in thecentral chamber and/or one or more of the other chambers.
 5. A containeraccording to claim 1 in which the internal cavity is provided with acorrespondingly shaped single unit internal container comprising fourside walls and a base.
 6. A container according to claim 5 in which theinternal container is divided up into a series of chambers.
 7. Acontainer according to claim 6 in which the internal container isdivided by one or more elements crossing the internal cavity orcontainer.
 8. A container according to claim 6 in which the internalcontainer is divided by one or more sleeves.
 9. A container according toclaim 8 in which the sleeves are encased in neutron absorbing material.10. A container according to claim 8 in which the neutron material is aresin.
 11. A container according to claim 10 , wherein the resin isintroduced around the sleeves as a liquid during manufacture.
 12. Acontainer according to claim 1 in which the insulating material isprovided in a series of discrete layers with one or more base layersand/or one or more wall layers for each wall.
 13. A container accordingto claim 1 in which the insulating layer is at least thermallyinsulating or neutron absorbing.
 14. A container according to claim 5 inwhich the internal container is made of steel.
 15. A containeraccordingly to claim 14 wherein the steel is boronated steel orstainless steel.
 16. A container according to claim 5 in which internalvolume is divided up into nine substantially equivalent chambers orsleeves.
 17. A container according to claim 6 in which the fuelcontainers comprise cylindrical drums received in one or more of thechambers.
 18. A container according to claim 6 in which fuel containersare provided in more than three of the chambers.
 19. A containeraccording to claim 1 in which one or more of the chambers are providedwith a neutron absorber.
 20. A method of transporting and/or storingnuclear fuel comprising placing nuclear fuel in a container according toclaim 1 .